1. Field of the Invention
The present invention generally relates to methods for altering the physical properties of materials and, more specifically, to methods for sonically treating sintered polymers to selectively reduce their void volume.
2. Background Information
Various assays are available to monitor medical conditions at home or in a clinical setting. Such assays often use chemically treated test strips that can react with specific analytes in the body fluids of patients. For example, blood glucose levels can be monitored using test strips that react with glucose in blood samples, causing a color change on the strips. By observing the degree of color change, patients under a diabetes-management regimen can monitor their glucose levels. If the levels are abnormally high, they can then take appropriate steps such as diet management or self-administration of insulin. Failure to monitor glucose levels can result in high glucose levels, leading to cardiovascular disease and degeneration of the kidneys, retinas and nervous system.
When using a test strip device, sufficient sample must be applied to ensure an accurate result. If insufficient sample is applied, the reaction may fail or react incompletely, yielding a misleading measurement. Even when sufficient sample is applied to the strip, it may not absorb the sample at once, leaving a pool of liquid to rest until eventually absorbed. Until the sample is completely absorbed, it risks being spilled or scattered by inattentive handling of the device, which can also result in a misleading measurement.
Previous devices have sought to speed the absorption of liquid samples by providing a porous layer over the test strip. When the sample is applied to such a layer, the porous structure allows relatively quick absorption so that a pool of sample does not remain on the surface for long. As the sample is absorbed, it passes through the pores by capillary action until it reaches the test strip underneath. Thus, the layer can be said to be a "receiving layer" for absorbing the liquid sample and allowing it to migrate to the test strip.
Unfortunately, a larger volume of sample is needed when using such a receiving layer. Because a certain amount of sample is retained in the pores of the receiving layer, the sample never completely migrates to the test strip. Instead, a significant fraction of the sample can spread to peripheral areas of the receiving layer, where it is retained in the pores. Unless larger volumes of sample are applied the receiving layer, the test strip may not receive sufficient sample to yield an accurate measurement. Thus, while a receiving layer speeds absorption of the sample and reduces spillage, this benefit is partially offset by requiring the application of larger sample volumes.
Applying larger samples of body fluids is practicable when the sample is easy to obtain, for example with urine or saliva, but it can be problematic when obtaining the sample is difficult or painful. When the sample to be tested is blood, the sample is typically obtained by puncturing the skin and then pressing the skin to apply drops to the test strip device. If insufficient blood is produced, the patient must repuncture the skin until sufficient blood is obtained to yield an accurate measurement from the test strip device. Obtaining sufficient blood for testing can therefore be difficult when patients have poor circulation and can be especially traumatic with young patients. Thus, the need to obtain larger samples of blood can deter patients from regularly using test strip devices, leading to ineffective compliance with their disease-management regimens.
Thus, there is a need for a layer for receiving a liquid sample where the retained volume is reduced, thereby minimizing the amount of sample necessary. The present invention satisfies this need and provides related advantages as well.